San Antonio recorded its first triple‑digit day on June 16, reaching 101°F with a heat index of 115°F. As excessive heat warnings continue and air quality declines, the region faces one of the hottest and driest summers on record…yet again.
Since early June, San Antonio has had only five “Good” air quality days (AirNow.gov). Rising temperatures, worsening drought, and continued canopy loss are accelerating ozone pollution.
The American Lung Association’s State of the Air Report ranks San Antonio 23rd worst for high ozone days out of 227 metropolitan areas. Bexar County received a failing F grade, with communities of color disproportionately impacted.
Trees are one of the most effective natural defenses we have. San Antonio is losing this
defense.
High ozone levels can be dangerous to both human health and the environment. Ozone is a gas composed of three oxygen atoms (O3) and is a major component of smog. While ozone in the stratosphere plays a crucial role in protecting us from harmful ultraviolet radiation, ground-level ozone is a pollutant.
What High Ozone Actually Means
Ground‑level ozone (O₃) is a harmful pollutant formed when heat, sunlight, and emissions mix. Unlike protective ozone in the stratosphere, ground‑level ozone damages human health.
Health Impacts of Ozone Exposure
● Respiratory irritation: coughing, throat discomfort, chest tightness
● Worsened asthma and increased respiratory infections
● Reduced lung function, especially for people with asthma, COPD, or bronchitis
● Cardiovascular strain: increased risk of heart attacks and strokes
● Higher susceptibility to allergies and pulmonary diseases
Children, older adults, and individuals with respiratory conditions are most at risk.
Why San Antonio Ranks Poorly
San Antonio’s ozone challenges stem from multiple environmental stressors:
● Extreme heat accelerates ozone formation
● Rapid development removes tree canopy and increases emissions
● Impervious surfaces trap heat and worsen air quality
● Drought conditions reduce natural cooling and intensify pollution
● Continued deforestation across Bexar County increases vulnerability
These factors create a feedback loop: hotter temperatures → more ozone → more health impacts → more environmental strain.
How Trees Reduce Ozone Exposure
Trees mitigate ozone dangers through natural processes:
Phytoremediation
● Trees absorb ozone through leaf stomata
● Ozone breaks down into oxygen inside the tree
Air Quality Improvement
● Trees filter pollutants, including ozone precursors (NOx, VOCs)
● They reduce particulate matter that interacts with ozone
Cooling Effect
● Shade lowers surface temperatures
● Reduced heat slows ozone formation
Ecosystem Health
● Cleaner air supports healthier plants, wildlife, and communities
Trees are not a complete solution, but they are a critical part of one.
What Happens if Canopy Loss Continues
Without intervention, Bexar County will face:
● more high ozone days
● increased respiratory and cardiovascular emergencies
● worsening drought impacts
● higher medical costs
● hotter neighborhoods
● greater strain on vulnerable communities
The F grade reflects a trajectory that will worsen unless canopy loss is addressed.
What Bexar Branches is Doing
Bexar Branches is working to:
● restore tree canopy
● identify high‑risk neighborhoods
● reduce heat exposure
● educate residents
● partner with local leaders
● advocate for long‑term environmental resilience
Every tree planted reduces future ozone exposure.
Learn More & Take Action
To help your trees survive hotter, drier summers:
● Texas Forest Service – Tree Watering Tips
● SAWS Drought Restriction & Watering Rules
● Bexar County Water Control & Improvement District
We can all do our part to be responsible stewards of our environment.
Thank you for all you do!
